Determination of the absolute configuration of the glucosinolate methyl sulfoxide group reveals a stereospecific biosynthesis of the side chain.
Glucosinolates are plant metabolites containing an anionic nitrogeneous thioglucosidic core structure and a structurally diverse amino acid-derived side chain, which after hydrolysis by thioglucohydrolases (myrosinases) afford biological active degradation products such as nitriles and isothiocyanates. Structural diversity in glucosinolates is partially due to enzymatic modifications occurring on the preformed core structure, like the recently described oxidation of sulfides to sulfoxides catalyzed by a flavin monooxygenase identified in Arabidopsis thaliana. The enzyme product, 4-methylsulfinylbutylglucosinolate, bears a chiral sulfoxide group in its side chain. We have analyzed the epimeric purity of 4-methylsulfinylbutylglucosinolate by NMR methods using a chiral lanthanide shift reagent. The absolute configuration of the sulfoxide group has been established by comparing the 1H NMR spectra of the two sulfoximine diastereomers of natural 4-methylsulfinylbutylglucosinolate. According to our data, 4-methylsulfinylbutylglucosinolate isolated from broccoli and A. thaliana is a pure epimer and its sulfoxide group has the RS configuration. The product of the A. thaliana flavin monooxygenase has these same properties demonstrating that the enzyme is stereospecific and supporting its involvement in glucosinolate side chain formation.
Vergara
Fredd
F
Max-Planck-Institute for Chemical Ecology, Beutenberg Campus, Hans-Knöll-Strasse 8, D-07745 Jena, Germany.
Wenzler
Michael
M
Hansen
Bjarne G
BG
Kliebenstein
Daniel J
DJ
Halkier
Barbara A
BA
Gershenzon
Jonathan
J
Schneider
Bernd
B
D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism; D001937:Brassica / Q000737:chemistry; D005961:Glucosinolates / Q000096:biosynthesis* / Q000737:chemistry* / Q000302:isolation & purification; D007202:Indicators and Reagents / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D006899:Mixed Function Oxygenases / Q000378:metabolism; D012680:Sensitivity and Specificity; D013237:Stereoisomerism; D013454:Sulfoxides / Q000737:chemistry*
D005961:Glucosinolates; D007202:Indicators and Reagents; D013454:Sulfoxides; D006899:Mixed Function Oxygenases